Flexible defibrillation electrode of improved construction

ABSTRACT

An implantable defibrillator lead comprises a flexible core onto which is wound helically wound coils to form an electrode. These electrode coils are partially encapsulated by a flexible matrix which holds them in their wrapped position around the core. Due to its coiled coil structure, this electrode provides improved flexibility, and can be used endocardially, intravascularly, epicardially, or subcutaneously. The electrode may function alternately as a defibrillation electrode and as a sensing electrode in a lead with a separate pacing electrode.

FIELD OF THE INVENTION

This invention relates to medical electrical stimulation electrodes ingeneral and to implantable defibrillation electrodes in particular.

BACKGROUND OF THE INVENTION

It is well known that cardiac arrhythmias such as ventricularfibrillation may be controlled with devices such as implantabledefibrillators. Many different types of defibrillation electrodes havebeen suggested over the years, as can be seen from the followingexamples. In this discussion, no distinction will be made betweencardioversion and defibrillation; both will be referred to asdefibrillation.

U.S. Pat. No. 3,942,536 issued to Mirowski et al. discloses anintravascular bipolar catheter electrode system wherein each of twoelectrodes is composed of a plurality of spaced, low impedance rings. Asimplanted, the first electrode is located within the right ventricle(RV) and the second electrode is located in the superior vena cava(SVC).

In U.S. Pat. No. 4,161,952 issued to Kinney et al., a catheter electrodehas a coil of wound spring wire, with filler material beneath andbetween individual turns of coil such that only the outside of the woundwire is exposed to the patient's body. It is designed to reside in orabout the heart, as in the SVC or in the coronary sinus (CS).

U.S. Pat. No. 4,922,927 issued to Fine et al. teaches the use of tightlywound wire forming a tight coil on a support that is flared to provide agreater diameter along its midsection than at its ends, to form an RVelectrode. A copper-zirconium alloy wrapped with tantalum and coatedwith iridium oxide is suggested for the tightly wound wire,

Other types of transvenously placed leads are disclosed in U.S. Pat. No.4,998,975 issued to Cohen et al. One lead is placed through the heartwall, and into the pericardial space, and another is placedendocardially in a conventional manner. Both leads are shown withseveral embodiments, with the examples of general electrode constructionbeing to expose a section of the conductor coil, or to use ringelectrodes similar to those used in conventional bipolar pacemakerleads. Cohen et al. also describe two methods for steering more currentto a selected region of the heart. The first method is to apply variousvoltages to the connectors of each of four electrodes. The second methoduses the resistance of conductors, both between connector and electrode,and between two electrodes on the same lead, and the body tissueresistance between electrodes on different leads, to form a voltagedivider, thus creating a different potential at each electrode.

Another lead system patent, U.S. Pat. No. 5,007,436 issued to Smits,describes electrodes of both J and straight configurations, for use inthe RV, right atrium, great cardiac vein, or CS. The fabrication methodssuggested use close wound conductive coils mounted exterior to anelongated insulative sheath, or the method of Kinney et al.

Spiral shaped electrodes for endocardial, epicardial, orextrapericardial implantation are described in Hell, Jr. et al., U.S.Pat. No. 5,016,808, Fogarty et al., U.S. Pat. No. 4,860,769, and Hauseret al., U.S. Pat. No. 5,052,407. The electrodes of these patents usevarious construction techniques, including electrodeposition or vapordeposition onto a plastic tube, helically wound wire (round or ribbon,unifilar or multifilar, single or double helix) or conductive rings on aflexible insulating portion, and conductive screen wrapped around atubular body.

Other defibrillation leads are disclosed in Mehra et al., U.S. Pat. No.5,144,960, and in Bardy et al., U.S. Pat. No. 5,174,288.

Endotak SQ Model 0048 (Cardiac Pacemakers Inc., St. Paul, Minn., USA),described in "A Subcutaneous Lead Array for Implantable CardioverterDefibrillators" by Jordaens et al., published in PACE, Vol. 16, July1993, Part I, is an electrode system consisting of three conductiveelements that can be subcutaneously inserted. The conductive elements ofthis "array lead" are made of electrically common multifilar coil,joined in a silicone yoke, and separately introduced with a leadtunneler and peel-away sheaths.

As defibrillator technology improves and the demand for defibrillatorsincreases, it becomes increasingly desirable to have leads availablethat are easily implanted. Any implantable defibrillation electrode mustbe capable of withstanding repeated flexing over a long period of time.In addition, the electrode must have sufficient surface area todischarge high amounts of energy for effective defibrillation, and mustmaintain its electrical integrity. The electrode must be ofbiocompatible materials, as well as of a shape that avoids tissuedamage.

SUMMARY OF THE INVENTION

The present invention provides a lead with an improved electrode designfor use with an implantable defibrillator system. In the preferredembodiment, a transvenous electrode is constructed from six tinyplatinum iridium space wound coils, space wound onto a silicone rubbertube, molded over with silicone rubber, then partially exposed byabrading away the molded silicone by grit blasting with sodiumbicarbonate. This electrode exhibits a high degree of flexibility andtherefore can be positioned quickly and easily within the rightventricle, right atrium, or superior vena cava, for example. Itsflexibility also permits insertion of a curved stylet to aid inplacement. Because of its flexibility, it can adapt to the complexmovement of the heart, and will not perforate the endocardium. Becauseof its coiled coil structure, the wire within the electrode flexes verylittle with electrode movement; therefore, the fatigue life is high. Theuse of small coiled coils may provide an electrode having a resistancegreater than about one ohm. While prior art systems attempt to minimizeelectrode resistance, this feature is used to advantage with the presentinvention wherein current flow from the electrode may be controlled ormodified by changing the location where the lead conductor iselectrically connected to the electrode.

In an alternative embodiment, this electrode construction can be used ona lead designed for epicardial placement.

In a third embodiment, an electrode of this construction can be used ona lead designed for subcutaneous placement.

It is thus an object of the present invention to provide a lead with animproved electrode for an implantable defibrillator.

It is a further object of the invention to provide a lead requiring lesstime for implantation.

It is an additional object of the invention to provide a lead with anelectrode that is more flexible and fatigue resistant than existingelectrodes.

It is another object of the invention to provide a lead with anelectrode that is easily manufactured.

It is another object of the invention to provide a method of electrodeconstruction that could be used to enhance the performance of the leadconfigurations of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present invention may be morereadily understood with reference to the following detailed descriptiontaken in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 illustrates the defibrillation electrode of novel construction ofthe present invention;

FIG. 2 is a detail view, partially cut away and partially in section, ofthe distal connection of the lead of FIG. 1;

FIG. 3 is a detail view of the distal end of the electrode coil of FIG.1;

FIGS. 4A and 4B illustrate the electrode of FIG. 1 during twomanufacturing steps;

FIG. 5 illustrates an alternative embodiment of the invention whichincludes a pacing electrode, and uses the novel electrode for bothdefibrillation and sensing;

FIG. 6 shows a sectional view of the distal end of the lead of FIG. 5;

FIG. 7 shows a detail view of the electrical connection of the lead ofFIG. 5;

FIG. 8 shows a cross sectional view of the proximal end of the electrodeof FIG. 5;

FIG. 9 illustrates one step in the manufacture of the lead of FIG. 5;

FIG. 10 shows a lead implanted in the heart that includes twodefibrillation electrodes and a pacing electrode;

FIG. 11 shows a J-shaped lead;

FIG. 12 shows a spiral-shaped lead and means to deploy it; and

FIG. 13 shows a detail view of an electrode connection of a lead withseveral electrodes in parallel for subcutaneous implantation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a lead 18 having an electrode 20 electrically connected toa conductor coil 30 in two locations. The first connection 34 is at thedistal end of electrode 20, and the second connection 36 is at theproximal end. These connections can be welds, crimps, and the like, inany combination. The conductor coil 30 is in turn electrically connectedto connector 32 for coupling with a pulse generator such as the typedescribed in U.S. Pat. No. 5,007,422 to Pless et al., which is assignedto the assignee of the present application. The lead body diameter isgenerally about 2.5 to 4.5 mm.

FIG. 2 shows a detail view of the distal connection of the lead 18 ofFIG. 1. Electrode 20 is shown to be constructed of many (six) electrodecoils 24 helically wound around a flexible tubular supporting core 22,which may be either electrically conductive or insulative, and may beextruded or molded. This structure has elastomeric material 28, whichalso may be conductive or insulative, partially encapsulating theelectrode coils. The many electrode coils increase conductivity andredundancy. One method of achieving this structure is to completelyencapsulate the wrapped electrode coils, then abrade away the surface topartially expose the coils using the method of Mar et al., U.S. Pat. No.5,226,260, which is assigned to the assignee of the present applicationand which is incorporated herein by reference. A conductor 30 extendsthrough the lumen of core 22, making connection 34 at the distal end ofelectrode 20. Conductor 30 is crimped to a sleeve 31 and to a pin 33.The distal ends of electrode coils 24 are melted into balls 27, whichare then welded to sleeve 31, forming an electrical connection to theconductor coil. This connection is also described in U.S. patentapplication Ser. No. 08/126,291, filed 24 Sept. 1993 by Mar, for a"Defibrillation Electrode Connection" which is assigned to the assigneeof the present application. The connection 34 is then covered by aprotective cap 35, which may be electrically conductive or insulative.Protective cap 35 seals the electrode connection from body fluids.Conductor coil 30 forms an inner lumen 38 through which a stylet may beplaced to stiffen the lead during implantation. Pin 33 serves both as asupport for coil 30 and sleeve 31 for crimping, and as a stop for thestylet.

FIG. 3 shows that each electrode coil 24 is made from a helically woundmetal wire 26, which may be round or flat in cross section. This wiremust be very strong, fatigue resistant, conductive, corrosion resistant,and biocompatible. Platinum iridium is one example of such a material.Electrode coil 24 is shown without an inner core; however, a thin wireor plastic filament could be located within coil 24 to provide eitherincreased electrical conductivity, mechanical redundancy, or both. Thefilament could be metal or nylon, for example. In order for the lead tobe sufficiently thin to be transvenously implantable, electrode coils 24should be between about 0.2 and 0.4 mm, and wire 26 should be about 0.05to 0.10 mm in diameter. Close winding of wire 26 into electrode coils 24provides more exposed metal for charge transfer to tissue. However,space winding decreases the lengths of wire in the coils, decreasing endto end electrode resistance. Additionally, space winding provides moresurface for matrix material to mechanically stabilize coils and allowsfor a substantial volume of matrix material that can flex with the heartand body motion instead of pulling away from the coils. Therefore, acertain amount of space is preferred, typically one-half to one wirediameter space between wires. Similarly, electrode coils 24 can be closeor space wound onto core 22. The same general principles apply. Thedistal end of each electrode coil 24 is melted into a ball 27, whichprovides more volume of material to form a strong and reliable crimp orweld. This melted ball structure works particularly well when made of anoble material such as a platinum iridium alloy. A hydrogen torch, alsocalled a "water welder", is one suitable means for melting the coil toform the ball. This device dissociates water into hydrogen and oxygen,then burns the hydrogen to form water again. This process burns cleanly,without incorporating byproducts into the melting coil, which isimportant for maintaining biocompatibility and material consistency forany subsequent welding.

FIGS. 4A and 4B illustrate the process by which electrode coils 24 areembedded in elastomeric material 28, preferably silicone rubber. FIG. 4Ashows electrode coil 24 as molded over by elastomeric material 28. FIG.4B shows the structure of FIG. 4A, after a portion of elastomericmaterial 28 has been abraded away to partially expose electrode coil 24.The level of material removal is controllable. The more metal exposed,the greater the electrode surface area for defibrillation, but the lessmaterial for providing mechanical stability.

FIG. 5 shows a lead 18' with a pacing electrode 44, and lo electrode 20which is used alternately for defibrillation and for sensing. Pacingelectrode 44 may be of any of the numerous constructions known in theart. A fixation mechanism 45 is shown as tines, but may be any known inthe art, including a screw used for both pacing and fixation. Pacingelectrode 44 is electrically connected to a pacing conductor coil 40,which is in turn connected to a pacing connector 43. Electrode 20 iselectrically connected at connection 34 to conductor coil 30, which iselectrically connected to both defibrillation connector 32 and a sensingconnector ring 39.

FIG. 6 shows a detail view of the distal end of the lead of FIG. 5.Electrode 20 is shown to be constructed of a plurality of electrodecoils 24 helically wound around flexible tubular supporting core 22.This structure has elastomeric material 28 partially encapsulating theelectrode coils. Conductor 30 extends through the lumen of core 22,making connection 34 at the distal end of electrode 20. Conductor 30 iswelded to the face of sleeve 29, as described in U.S. patent applicationSer. No. 08/018,832, filed Feb. 18, 1993 by Bush et al., for an"Electrical Connection for Medical Electrical Stimulation Electrodes"which is assigned to the assignee of the present application and whichis incorporated herein by reference. The distal ends of electrode coils24 are melted into balls 27, and are then welded to sleeve 29, formingelectrical connection 34 to the conductor coil. A pacing conductor coil40 extends through the lumen of tubular core 22 and is electricallyinsulated from conductor coil 30 by an insulator 42. Pacing conductorcoil 40 is shown connected by a crimp connection to pacing electrode 44and a crimp pin 41; this connection may alternatively be a weld.

FIG. 7 shows a detail view of electrical connection 34. The distal endof conductor coil 30 has been welded to the face of sleeve 29. Electrodecoils 24 have had their distal ends melted into balls 27, then welded tothe outside surface of sleeve 29.

FIG. 8 shows a cross sectional view of the proximal end of electrode 20.Two groups of electrode coils 24 have their proximal ends melted intoballs 27' to provide electrical redundancy. Molded electrode core tube22 has two pockets 25 in its proximal end into which balls 27' areplaced prior to wrapping electrode coils 24 onto tube 22. Afterelastomeric material 28 is applied, an electrical insulation 37 isjoined to electrode 20 using a joining material 47, for example siliconerubber. A mandrel is used to keep the lumen open during this process, sothat the conductor can be passed through the joint and connected at thedistal end of electrode 20.

FIG. 9 shows one group of three electrode coils 24 with proximal endsmelted into ball 27'. This group of three electrode coils can be woundonto a tube such as core tube 22 of FIG. 8 in several ways. Thepreferred method is to insert a mandrel into a molded core tube, placethe mandrel into a lathe-type coil winder, insert one group of threeelectrode coils 24 into each of two pockets of the tube, then use thecoil winder to wind the electrode coils 24 around the tube. After theelectrode coils 24 are wound onto the core tube, elastomeric materialmay be compression molded over the coils and core. An alternative methodis to embed electrode coils 24 into uncured elastomeric material thathas been rolled into thin strips, then wrap the coil embedded strips ofelastomeric material around a core tube, then cure the elastomericmaterial. A third alternative is to apply uncured elastomeric materialto a cured core, then wind electrode coils 24 about the core, embeddingthem into the elastomeric material. Yet a fourth alternative is tomanufacture the core and elastomeric material portion simultaneously byputting uncured rubber onto a mandrel to form both portions; electrodecoils 24 are then embedded into the surface of the rubber, and therubber is cured.

FIG. 10 shows a lead 18" with two defibrillation electrodes, 20' and20", having opposite polarity, and a pacing electrode 44 as it ispositioned within a patient's heart. Electrode 20' acts alternately as adefibrillation electrode and as a sensing electrode. The lead is shownas situated in the heart, with pacing electrode 44 and distaldefibrillation electrode 20' in the right ventricle, and proximaldefibrillation electrode 20" located in the superior vena cava.

FIG. 11 shows a lead with a J shaped defibrillation electrode 20 andwith screw in tip 44', for use in the right ventricle or atrium, forexample. Screw in tip 44' can be used for pacing and fixation, or forfixation alone. The preferred method of manufacturing a J shaped lead isto start with a tubular core which has been molded in a J shape. The Jshaped tubular core is then straightened by inserting a mandrel into it.Then, electrode coils as described above are wound onto the straightenedcore. The tubular core and electrode coils are then reformed into the Jshape by removing the straight mandrel, perhaps lo replacing it with a Jshaped one. The tubular core with electrode coils is then molded overwith elastomeric material, holding the electrode coils in their final Jshape.

FIG. 12 shows a spiral electrode 20, and means for deploying it. Astylet 52 is inserted through lead 18"' and is used to push electrode 20through an introducer sheath 56.

FIG. 13 illustrates a lead with three electrodes 20, intended forimplantation subcutaneously on the left lateral part of the chest. Theyare of the same polarity, and are connected to a common node onconductor 30. Electrode coils 24 are connected at distal ends by meltedballs 27' and wound onto flexible cores 48. Flexible embedding material50 partially covers electrode coils 24. The proximal ends of electrodecoils 24 are all connected by melting them into ball 27". Ball 27" iscrimped into metal joining piece 58. Also crimped to metal joining piece58 is crimp sleeve 31 and conductor coil 30. A protective strain reliefmolding 60 encapsulates the entire connection.

Because the electrode coil wire is longer and thinner than the electrodeelements of the prior art, the electrode of the present invention can bemade with a certain amount of resistance along its length, say, 3 to 15ohms. This property of the electrode can be used to directdefibrillation energy to selected regions of the heart by careful choiceof connection locations of electrode to conductor. For example, if theelectrode 20 of FIG. 5 were placed with its distal end in the apex ofthe RV, current would be steered to the RV apex since that is where theconductor attaches to the electrode at connection 34. On the other hand,because of the electrode connections 34 and 36 on either end ofelectrode 20 of FIG. 1, the current distribution would be more evenalong the electrode length than in the electrode of FIG. 5, since thepotential is the same at either end, assuming a very low resistanceconductor 30. In this case, the end to end electrode resistance is alsoreduced, with the highest resistance being in the middle of theelectrode. The connection could also be made in the middle of theelectrode, instead of or in addition to the ends. With the electrodeconnected to the conductor in only the middle of the electrode and notthe ends, current density would be more even since end effects would bereduced. Several connections between the conductor and the electrode maybe made along the length of one electrode. This is desirable forreducing overall resistance, particularly when the electrode is long, asin the lead of FIG. 12.

The above has been offered for illustrative purposes only and is notintended to limit the scope of the invention of this application, whichis as defined in the claims below.

That which is claimed is:
 1. A body implantable lead including at leastone electrode having a proximal end and a distal end, comprising:aflexible tubular supporting core having a lumen therethrough; at leastone electrode coil helically wound about said core, said at least oneelectrode coil having a proximal end corresponding to said electrodeproximal end and a distal end corresponding to said electrode distal endand comprising at least one helically wound metal wire and beingconnected at one of said ends to a conductor; and a matrix ofelastomeric material partially encapsulating said electrode coil andholding said electrode coil in said helically wound position around saidcore.
 2. The lead of claim 1 in which said conductor is attached to aconnector for connection of said lead with an implantable defibrillator.3. The lead of claim 1 in which said core is insulative.
 4. The lead ofclaim 1 in which said core is conductive.
 5. The lead of claim 1 inwhich said wire is round in cross section.
 6. The lead of claim 1 inwhich said wire is flat and substantially rectangular in cross section.7. The lead of claim 1 in which said wire is made of a platinum iridiumalloy.
 8. The lead of claim 1 in which said matrix is insulative.
 9. Thelead of claim 1 in which said matrix is conductive.
 10. The lead ofclaim 1 in which said wire is between about 0.05 and 0.10 mm indiameter.
 11. The lead of claim 1 in which said at least one coil isbetween about 0.2 and 0.4 mm in outer diameter.
 12. The lead of claim 1in which said conductor is a coil that extends through the lumen of saidtubular core.
 13. The lead of claim 12 in which said conductor coil iselectrically connected to said electrode coil at said distal end of saidelectrode coil.
 14. The lead of claim 12 in which said conductor coil iselectrically connected to said electrode coil at both ends of saidelectrode coil.
 15. The lead of claim 12 in which said conductor coil iselectrically connected to said electrode coil at a location between saidproximal end and said distal end of said electrode coil.
 16. The lead ofclaim 12 in which at least a portion of said conductor coil forms aninner lumen capable of accommodating a stylet.
 17. The lead of claim 12in which at least a portion of said conductor coil forms an inner lumenthrough which extends an insulated conductor.
 18. The lead of claim 1 inwhich said wire is space wound.
 19. The lead of claim 1 in which saidelectrode coils are space wound about said tubular core.
 20. The lead ofclaim 1 in which said electrode is J shaped.
 21. A body implantable leadincluding at least one defibrillation electrode having a proximal endand a distal end, comprising:a flexible core; at least one electrodecoil comprising at least one helically wound wire; each said at leastone electrode coil being helically wound about said core, said at leastone electrode coil having a proximal end corresponding to said electrodeproximal end and a distal end corresponding to said electrode distal endand being connected at one of said ends to a conductor; and saidelectrode coil being partially embedded in flexible material and therebyheld in fixed position around said core.
 22. The lead of claim 21 andfurther including a plurality of said electrodes electrically connectedat a common node.
 23. A body implantable lead including at least onedefibrillation electrode comprising:a flexible core: at least oneelectrode coil helically wound about said core, said at least oneelectrode coil comprising at least one helically wound metal wire andbeing connected at one end to a conductor for connecting said electrodeto an implantable pulse generator; and wherein said electrode has aresistivity along its length greater than one ohm whereby currentflowing from said electrode differs depending on the location of theconnection between said conductor and said electrode.